The present invention relates to novel curing adhesive films useful to produce structural materials, particularly for making laminated panels, e.g., for panels useful for aircraft interiors, truck siding, or for laminates useful in printed or flexible circuit boards, or for a wide variety of structural uses. The invention is particularly useful in the manufacture of decorative laminated structural panels, such as those used in aircraft, boat, mobile home or other interiors. The inventions also comprises novel methods and articles of manufacture that utilize or comprise such compositions.
Structural laminates are well known in many different areas. For example, decorative laminates are integrally or screen printed materials commonly employed in the fabrication of commercial aircraft interiors. Such decorative laminates are typically applied to many interior surfaces of passenger aircraft for purposes of decoration. These materials have been produced by lamination of a curing adhesive film and a structural layer, typically a polyvinyl fluoride film such as Tedlar.RTM., available from E. I. DuPont de Nemours & Co. The laminate is then embossed to provide a decorative pattern. The adhesive film adheres to the Tedlar or other structural layer, and can also operate as an embossment composition, to hold the embossment in the structure, so that the laminated film retains its decorative embossed pattern while it is being further handled or manufactured, and when in place. Typically the Tedlar/adhesive structure is then adhered, through a further adhesive system, to panels, films, frames, struts, or other structural parts. The adhesive film not only preserves the texture imparted to the embossed film by the embossing or thermoforming operation, but preferably also can provide flame retardant properties to the formed laminate article.
Other structures are also known for producing structural laminates.
For example, "Double" decorative laminates are also used in aircraft interiors and are formed by casting a curing adhesive film onto a support film such as Tedlar and then placing another support film layer over the adhesive layer. The three layer stack of materials may then be laminated and embossed, with the embossed pattern primarily showing on one side of the resulting laminate. The embossed structure can then be adhered to a substrate, e.g., structural members such as ceiling or wall panels. The double layer of protective film guards against wear and tear from areas which typically receive substantial use.
Such structures and processes have suffered from a number of problems. For example, structural films such as Tedlar although flame treated to increase its surface adherability, are notoriously difficult to adhere to. Further, in order to fix the embossing in the structure in a way which would not be adversely effected by further processing steps, even where such processing is conducted at elevated temperatures, it is necessary to use an adhesive system which is thermosetting under conditions of use, i.e., which cure to form a film which holds the embossing, and which will not deform, distort or delaminate under elevated temperatures in further processing. For example, where the embossed material must then be attached to formed panels, e.g. using a vacuforming process, thermoplastic embossing films, or thermosetting embossing films which have not been cured, will lose the embossing pattern when subjected to vacuforming conditions.
See, e.g., U.S. Pat. No. 4,788,091 to Rossitto et al., which is incorporated herein by reference. As pointed out in that patent, another problem necessary to deal with in aircraft interiors is flame retardancy. In order to respond to that problem, the adhesive has to be able to accommodate whatever flame retardant system is utilized.
The laminating adhesive layer in the Rossitto patent was a material which required high cure temperatures, and extensive time at cure temperature in order to hold the embossing and adhere the adhesive to the structural (e.g. Tedlar) film. Other materials previously used, such as polyesters and polyurethanes, similarly suffered from high cure temperatures and times necessary to make the ultimate structure.
The high temperatures and dwell times required by previous systems such as that of Rossitto have necessitated slow, tedious and costly manufacturing processes in making the embossed laminates. Typically, a "sandwich" of materials is prepared in a stack and placed within a heated embossing press which applies pressure and temperature to the stationary stack for the period of time necessary to effect total cure. The sandwich of materials may suitably include, in succession, a textured sheet or blanket (e.g. fiberglass) that bears the decorative imprint to be embossed, a sheet of embossable material, e.g., Tedlar film having a nominal thickness of 1.5-2 mils, and a sheet of the uncured adhesive film. That layering can be repeated a number of times in the stack of materials to be pressed, with the adhesive film layers typically separated by a sheet of release paper or the like. This "sandwich" is then placed on the heated embossing press. The heat and pressure applied by the embossing press causes the adhesive film to adhere to the Tedlar sheet and to cure, and causes the pattern of the textured blanket to be imprinted into the laminate. Required conditions of such lamination and embossing have included pressures of about 100 psi and temperatures of about 320.degree. F. for between 10 and 20 minutes.
The thus formed laminate with decorative patterned surface can be affixed to the interior surface of an aircraft, and formed into panels, side wall stowage bins, etc., typically by a vacuum-forming application, during which the formed decorative laminate can be exposed to temperatures of up to about 250.degree. F. or more.
While that process can produce a suitable laminated product, the extended residence times of the layered sheets in the embossing press during lamination and embossing effectively limits throughput and adds substantially to manufacturing costs.
Other structural members which comprise laminates of various materials with thermosetting adhesives have also required high temperatures and dwell times, which effect the manufacture of the members. Moreover, unless the high curing temperatures and dwell times of the known thermosetting adhesive films are met in the processing, the structural integrity of the laminates produced can be severely adversely effected.
It thus would be desirable to have new compositions that could be used as an adhesive and as an embossing film.
It would be further desirable to provide such compositions which can be cured at lower temperatures and/or shorter times than current compositions. Such compositions would be highly useful in the fabrication of structural laminates, such as the decorative laminates for aircraft interiors.